This invention relates to an optical module package which is suited for use in packaging therein a laser diode for optical communication, in particular to be employed as an exciting light source of light direct amplification type emitting a wavelength of 0.98 .mu.m.
As shown in FIGURE, an optical module package 1 comprises a heat spreader attached through silver-brazing to the bottom of a frame 2, ceramic terminals 4 and leads 5 which are attached through silver-brazing to the side walls of the frame 2, and a seal ring 6 attached through silver-brazing to the top of the frame 2. This resultant silver-brazed structure is then subjected to an Au-plating, and thereafter a window (not shown) is attached by means of AuSn soldering to the rear end portion of a window frame 7 which is disposed at the front portion of the Au-plated frame 2. By the way, when an Au-plating is to be performed, an Ni-plating is generally applied as an underplating before the Au-plating.
After a laser diode (not shown), etc. are mounted on a predetermined inner portion of the optical module package 1 constructed in this manner, a cover (not shown) is seam-welded on the seal ring 6 attached to the top of the frame 2, thereby assembling an optical module.
Next, the constituent parts of the optical module package will be explained with reference to FIGURE.
The heat spreader 3 constitutes the bottom portion of the optical module package 1. This heat spreader 3 is made of a high heat conductive material, e.g. a CuW board whose surface is plated with Ni, thus rendering it to function as a medium for easily releasing the heat generated during the operation of the optical module into the external atmosphere.
The frame 2 constitutes the outer framework of the optical module package 1, and can be manufactured by means of an injection molding using an Fe--Ni--Co alloy (Kovar) or an Fe--Ni alloy. The window frame 7 can be molded integral with the main frame body by means of injection molding. This frame 2 can be manufactured also by a method wherein a square pipe is cut out at first thereby to form a main body to which a pipe functioning as the window frame 7 is soldered.
The ceramic terminals 4 can be attached to the side walls of the frame 2 by means of silver-brazing. As for the material for constituting the ceramic terminals 4, a multi-layer ceramic which is composed of plural alumina thin plates laminated with each other can be employed. This multi-layer ceramic can be manufactured by means of an ordinary sintering method. The lead connecting portion (electrode portion) of the ceramic terminals 4 is subjected to an Ni-plating after the metallization treatment thereof.
The leads 5 are a conductor medium electrically connecting the electric parts mounted inside the package with the external power source. The seal ring 6 is a counterpart part for seam-welding the cover, and may be formed of Kovar or an FeNi alloy. These leads 5 and seal ring 6 can be manufactured by means of etching or press-punching.
The window can be manufactured by a process wherein a sapphire body constituting the window is metallized at first and then covered thereon with a non-reflection coating.
Next, the method of manufacturing an optical module package using the aforementioned parts will be explained in details with reference to FIGURE.
First of all, the frame 2 is disposed via a silver braze on the surface of the heat spreader 3, the ceramic terminals 4 and the leads 5 are both disposed via a silver braze to contact with the side walls of the frame 2, and the seal ring 6 is disposed via a silver braze on the upper surface of the frame 2, respectively. Then, while each member is being retained in position by making use of a carbon jig, the resultant structure is heated in a mixed gas atmosphere containing hydrogen (hereinafter referred to simply as a hydrogen-containing atmosphere) thereby to perform the silver brazing thereof.
The entire structure thus brazed with this silver braze is subjected to an Au plating. Any portions of the structure which may cause an inconvenience due to the existence of this Au plating such as the front end face 8 of the window frame to which the bracket of an optical fiber is to be attached should be polished in advance so as to remove the Au plating. Thereafter, the window is attached by means of soldering to the rear end portion of the window frame 7 which has been mounted on the front portion of the frame. This soldering is performed using an AuSn solder and in a hydrogen-containing atmosphere.
Since the silver brazing and the soldering of the window using an AuSn solder are all performed in a hydrogen-containing atmosphere according to the aforementioned manufacturing method of an optical module package, it is inevitable that a large quantity of hydrogen is absorbed in the parts made of Kovar or FeNi alloy, and that a large quantity of hydrogen is absorbed in the Au-plating layer during the plating process. It is also inevitable that a large quantity of hydrogen gas is absorbed in advance in the parts made of Kovar or FeNi alloy, since the heat treatment at the occasion of working of raw materials as well as the sintering of molded products after the injection molding thereof are all performed in a hydrogen-containing atmosphere.
The hydrogen gas absorbed in the parts made of Kovar or FeNi alloy, or in the Au-plating layer is caused to be released gradually due to the heat generated at the occasion of seam-welding the cover to the frame or due to the heat generated in the operation of the optical module. As a result, the hydrogen gas thus released is caused to react with the oxygen gas included in a very small quantity inside the package, thus producing water. When this package is exposed to a low temperature, this produced water is caused to condense in the package thereby to form dew drops, thus badly affecting the operation of the optical module and deteriorating the reliability of the optical module.
In view of these problems, a method has been proposed (Japanese Patent Unexamined Publication No. H7-147457) wherein the package is subjected, after the soldering of the window, to a heating treatment in the air atmosphere or nitrogen gas atmosphere at a temperature of 150.degree. C. for 200 hours or so, thereby allowing the absorbed hydrogen to be released from the package.
However, this method is accompanied with the problems that since the heating time is relatively long, the productivity may be deteriorated, and that the front end face portion of the window frame where the Au plating has been removed in advance is oxidized thereby inviting the discoloration thereof, thus making it difficult to satisfactorily perform the subsequent spot welding of the fixing bracket of an optical fiber.
It is also conceivable, as a method for overcoming the aforementioned problems, to anneal the package at a high temperature and for a short time in vacuum or in an inert gas atmosphere. However, this method is unpractical, since it will invite the melting of the AuSn soldering which is low in melting point as well as the denaturing of the Au plating layer due to the diffusion thereof.